Electric gaseous discharge device



Nov, 8, 1938. w. ELENBAAS ELECTRIC GASEOUS DISCHARGE DEVICE Filed 001:. 15, 1937 INVENTOR Willem. Eenb 5 BY $4 5. Jul

AT ORNEY 50 gone into extensive use.

Patented Nov. 8, 1938 UNITED STATES PATENT OFFICE Willem Elenbaas, Eindhoven, Netherlands, assignor to General Electric Company, a corporation of New York Application October 15, 1937, Serial No. 169,162

In Germany November 10, 1936 3 Claims.

The present invention relates to electric gaseous discharge devices generally, and in particular to devices operating with a relatively high vapor pressure.

5 A particular object of the invention is to provide an electric gaseous discharge device of high luminous efiiciency. A further object of the invention is to provide a lamp of long useful life. Still other objects and advantages of the invention will appear from the following detailed specification or from an inspection of the accompanying drawing.

The invention consists in the new and novel structure hereinafter set forth and claimed.

Among the illuminating devices of recent years, the high-pressure mercury-vapor discharge tubes are of great importance. The modern lamps of this type commonly have a cylindrical discharge bulb containing a small quantity of mercury.

These bulbs are provided with solid thermionic electrodes which are generally covered with materials of a high electron emissivity (especially earth alkali metal oxides). In order to facilitate ignition, a quantity of rare gas is also ordinarily placed in this bulb. The actual discharge bulb is generally surrounded by a glass cover, while the space between the discharge bulb and. the cover is evacuated, or is filled with a gas (for instance, nitrogen, rare gas, or air).

The discharge of these lamps has the character of a high-pressure discharge. In other words, the discharge is constricted as a result of the high vapor pressure that is developed, so that it does not fill the entire cross-section of the discharge bulb. At the same time, the burning voltage of the discharge is relatively high, ordinarily having a value which is many times as great as the socalled initial burning voltage, that is, of the burning voltage which occurs immediately after the ignition. The mercury-vapor pressure during operation in the lamps of the type which were first developed is approximately one atmosphere. These lamps are manufactured in different sizes, and the power consumption is from approximately 150 watts to several kilowatts.

Recently, mercury-vapor discharge tubes which operate with a much higher mercury-vapor pressure, that is a pressure which is generally considerably higher than 10 atmospheres, have also These lamps have a diameter which is much smaller than that of the lamps previously referred to in which the operating vapor pressure is approximately one atmosphere. The internal diameter of these new 55 lamps, which are made of quartz, is of the order .these lamps is dependent upon the particular relationship of these various characteristics. The present invention is directed to the production of lamps within this range having the highest attainable eificiency and a long useful life.

In the design of any of these lamps two factors are usually fixed at the start. Thus the wattage consumption of the lamp is a matter of arbitrary choice, and the voltage drop within the burner is a substantially fixed fraction, of 20 the. order of a half or two-thirds. of the voltage of the line on which it is intended to operate the lamp. With these two factors settled, however, there is still a vast number of combinations of length. diameter and operating pressure that will meet the predetermined conditions, but not with the same efiiciency or useful life. I have discovered, however, that the maximum efiiciency, together with a long useful life of at least 2000 hours is produced in a lamp designed to operate with B watts energy consumption with VB volts across the lamp itself where the internal d ameter of the discharge envelope is made equal, in millimeters, to

2 0.3 35 2.3 In addition, I have found that a lamp having an internal diameter which meets the foregoing condition combined with a length as given below 40 will operate with a quiescent discharge, even when the arc tube is vertical, thus avoiding the turbulence and; wobbling of the arc stream which is otherwise an undesirable characteristic of many of the lamps operating at relatively high pressure. This eliminates the necessity of using baiiles and the like to impart stability to the arc path. While it is desirable from all these standpoints that the diameter should be close to the value indicated by the foregoing formula, I have found that satisfactory results can be attained with a deviation therefrom of 15 per cent, and in some cases of even a maximum of 20 per cent, although I prefer to keep the deviation less than 15 per cent.

With the diameter thus determined, however, I have dmcovered that it is essential to the attainment of the desired eiilciency, stability and when B is again the energy consumption, in watts, and Be the arc voltage, in volts. Although by far the best results are attained with an arc path of the length determined by this formula, it has been found that deviations up to per cent can be permitted with satisfactory results.

When, in the case of a given power consumption and lamp voltage, the diameter and the length of the discharge path have been determined in this manner, then the other data of the lamps are also readily calculated. Thus with a given lamp voltage and length of the discharge path, the gradient is determined by dividing this voltage less the cathode fall by the length of the discharge path. Only one certain mercury vapor pressure will give this gradient with the designed diameter and power consumption. The vapor pressure is determined by the coldest point of the discharge bulb, or in. case the quantity of mercury is limited to such an extent that the lamp operates with an unsaturated vapor, itis determined by the quantity of mercury placed in the lamp. These values must for that reason be selected in such a way that the required gradient is obtained, using well known formulae.

The wall thickness of the discharge bulb is preferably made approximately where d is the internal diameter in mm., in order to withstand the internal pressure.

The above formulae apply only in those cases in which the internal diameter is more than 7 mm., and are of particular importance for lamps with a power consumption of more than 75 watts. They have no validity for lamps which are cooled artificially, for instance, with running water.

The drawing shows by way of example a discharge tube according to the invention.

The discharge bulb I consists of a cylindrical quartz tube with an internal diameter of 15 mm., and contains two activated thermionic electrodes, 2 and 3, which are arranged close to the ends of the bulb and consist of coil-shaped tungsten wires which are coated with an earth alkali oxide. As shown, these electrodes are of the type heated by the discharge. The spacing of the electrodes 2 and 3 is 4 cm. The dis charge bulb is filled with argon, which at room temperature has a pressure of the order of 10 mm. There is further placed in the bulb a small quantity of mercury, which evaporates completely during operation so that the lamp operates with unsaturated vapor.

The discharge bulb is attached by means of the current supply wires 4 and 5 to the stem press 6 of the glass bulb I which has the shape of an ordinary incandescent bulb. The space between the discharge bulb I and the bulb I is preferably filled with nitrogen, which at room temperature has a pressure of approximately 50 cm. The bulb is provided with a conventional screw base 8.

Any usual means to facilitate the ignition, such as a suitably connected auxiliary electrode in the vicinity of one of the glow electrodes or a thin metal wire wound around the tube approximately at the center of the tube, is provided where desired.

The lamp is intended to be connected to a 220 .volt source of commercial frequency, in series with a choke coil 8, as shown. The power consumption of the tube is 250 watts and the buming voltage (in the case of normal operation after equilibrium is attained) is 120 volts. The internal diameter of the discharge bulb agrees with the above-mentioned formula, while the length of the discharge path is only slightly smaller than the valve calculated by means of the formula indicated for this length, and is within the. limits oi! the permissible deviation.

The output of visible light of the described lamp is 50.8 international lumens per watt, while it the discharge path is increased to a length of 5 cm., then the light output of this modified lamp is reduced to 49.4 international lumens per ,watt for the same power consumption (250 watts) and the same operating voltage (120 volts).

The wall thickness of the'discharge bulb was calculated by means of the formula and amounts to 1.3 mm. However, it is possible to permit large tolerances in the wall thickness.

The discharge lamp is arranged, where desired, in a reflector of suitable shape. The lamp is not cooled artificially; the developed heat is dissipated by means of natural cooling. When the lamp is to be used for the emission of ultraviolet rays, the cover I is made of a material which permits these rays to pass.

While I have illustrated my invention by reference to a particular embodiment thereof, it is to be understood that it is not limited thereto, but that various omissions, substitutions and changes, within the scope of the appended claims, may be made therein without departing from the spirit of the invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, a source of electrical energy, a bailasting device and a tubular mercury vapor arc discharge device connected in series across said source, said bailasting device limiting the potential across said discharge device to Va volts when B watts energy is consumed in said device, the inside diameter of said discharge device being equal (in millimeters) to and greater than 7 mm. and the length of the discharge path within said device being equal (incentimeters) to value of this 2. In combination, a source of electrical energy, a bailasting device and a tubular mercury vapor arc discharge device connected in series across said source, said bailasting device limiting the potential across said discharge device to Va volts when 3 watts energy is consumed in said device, the inside diameter or said discharge device being equal (in millimeters) to 2 o.a-2o% 2.3 and greater than 7 mm. and the length of the discharge path within said device being equal (in centimeters) to o.s o.n Ti 25%.

3. In combination, a source of electrical energy, a ballasting device and a tubular mercury vapor arc discharge device connected in series across said source, said ballasting device limiting the potential across said discharge device to V1; volts when B watts energy is consumed in said device, the inside diameter of said discharge device being equal (in millimeters) to B2 2.3(VB)0.3 and greater than 7 mm. and the length of the discharge path within said device being equal (in centimeters) to the source of said vapor within the discharge being limited to such an amount that it is wholly vaporized when 13 watts energy is consumed in said device. WILLEM ELENBAAS. 

